A wide variety of halogenated organic compounds have been identified as being potentially hazardous to human health or to the environment. The safe destruction of these compounds in some waste materials is made particularly difficult by the nature of the waste, which may impede access to the hazardous compound for the purpose of treatment. The present invention relates to the treatment of a variety of hazardous halogenated compounds in waste materials comprised of asphalt, an example of which is potting compound contaminated with polychlorinated biphenyls (PCBs).
PCBs are a family of very stable halogenated organic compounds of which there are more than 200 individual compounds (sometimes known as congeners, identified by IUPAC numbers 1-209). PCBs are the product of the chlorination of a biphenyl structure, wherein one or more of the ten hydrogen atoms of a biphenyl are replaced with chlorine atoms.
PCB were often produced in commercial mixtures, such as Aroclors (trademark) sold by the Monsanto Chemical Company. PCBs were often used in mixtures with other halogenated organic compounds, such as trichlorobenzene or tetrachlorobenzene, for example in insulating fluids for electrical equipment (such mixtures may be referred to by the tradename Askarels). In various aspects, the present invention relates to processes for the decomposition of such compounds and mixtures.
PCBs are not easily destroyed by natural processes. Their use has been banned for environmental reasons due to the possible danger to the environment and inhabitants. PCBs are not easily biodegradable and will not disappear or decay to any extent by natural processes. Once they are formed, they can be destroyed only by special and generally expensive procedures.
Because they are stable, conduct heat well and are good electrical insulators while being fire resistant, PCBs have been used extensively in dielectric materials in electrical components such as transformers and capacitors. Although further use of PCBs for such purposes is generally prohibited by regulation in most jurisdictions, large quantities of these chemicals are present in existing equipment or in industrial waste, particularly in the electrical industry. In some jurisdictions, there are very large quantities of wastes in stockpiles awaiting disposal that have been identified as being contaminated with PCBs.
The longstanding nature of the problem of the disposal of organic halides is reflected by the fact that a significant number of innovative methods have been disclosed over a period of many years for disposing of PCBs and other organic halides, as for example are discussed in the following U.S. patents (which are incorporated herein by reference): U.S. Pat. No. 4,284,516 issued 18 Aug. 1981 to Parker et al.; U.S. Pat. No. 4,340,471 issued 20 Jul. 1982 to Jordan; U.S. Pat. No. 4,377,471 issued 22 Mar. 1983 to Brown et al.; U.S. Pat. No. 4,379,752 issued 12 Apr. 1983 to Norman; U.S. Pat. No. 4,379,746 issued 12 Apr. 1983 to Norman; U.S. Pat. No. 4,465,590 issued 14 Aug. 1984 to Adams; U.S. Pat. No. 5,592,844 issued 3 Jun. 1986 to Layman et al.; U.S. Pat. No. 4,636,309 issued 27 Jan. 1987 to Lalancette et al.; and U.S. Pat. No. 5,779,813 issued 14 Jul. 1998 to Plunkett.
While PCBs can be destroyed by incineration, high temperatures and controlled conditions are generally required, in order to avoid generation of PCB thermal decomposition byproducts that may be significantly more toxic than PCBs, such as polychlorinated dioxins and furans. PCBs also have been disposed of by burial, but the stability of these compounds gives rise to concerns about approaches to disposal that do not destroy the compounds themselves.
Capacitors containing PCBs were used in electrical equipment such as fluorescent light ballasts until they were prohibited by regulations. Many of these capacitors leaked PCBs into the ballasts during malfunction, thus contaminating the internal components of the ballast, such as the potting compound. The potting compound is typically a mixture of asphalt and sand (silica) that surrounds the electrical components in the ballast. Potting compounds may also include other ingredients such as waxes that modify properties such as the melt range of the potting compound and the adhesive characteristics of the asphalt. Asphalt is used primarily to provide an adhesive for the sand, which acts as an insulator and heat conductor. Some potting compounds may for example be made up of 35-50% silica for proper heat transfer, 50-65% percent asphalt and 0-10% wax.
The disposal of used PCB-containing electrical components such as capacitors and fluorescent light ballast assemblies has posed a problem to commercial and other institutions for some years, particularly in view of relatively recent regulations governing legal responsibility for their disposal and the environmental safety of the waste products of such disposal. The concomitant problems of enabling conservation or salvaging of the components and materials in the used ballasts by decontamination, reclamation and reuse, refurbishing or recycling of the materials therein (metals, wires and windings, plastics, etc.) have been largely ignored in light of the environmental concerns.
There is a longstanding need for alternative approaches to the decontamination of wastes containing halogenated organic compounds such as PCBs, particularly wastes that may be difficult to treat because they are composed of complex cementitious mixtures entraining the hazardous compounds. In such wastes, the interaction of the hazardous compounds with other compounds in the waste matrix may interfere with the accessibility of the hazardous compounds to treatment.